Condition control system



April 6, 1943. -r. K. GREENLEE ETAL 2,315,517

CONDITION CONTROL SYSTEM Filed March 7, 1936 2 Sheets-Sheet l INVENTORSv Theodore K. Green/ee, Gerald "(Ba/m, and Cori/0nd N. ODa

BY 46. W/ QAAU IJ ATTORNEYS 4 April 6, 1943. 'r. K. GREENLEE ET AL2,315,517

CONDITION CONTROL SYSTEM Filed March '7, 1936 2 Sheets-Sheet 2 INVENTORSTheodore K.Gr'en/e, Gerq/d IV. Balm,

ano/ Cori/and N. ODay ATTORNEYS Patented Apr. 6, 1943 CONDITION CONTROLSYSTEM Theodore K. 'Gr'eenlec, Rockford, 111., and Gerald W. Bohn andCortland N. ODay, Port Washington, N. Y., assignors to Barber-ColmanCompany, Rockford, 111., a corporation of Illinois Application March 7,1936, Serial No. 67.612

10 Claims.

This invention relates generally to condition control systems and insome of its aspects has to do more particularly with the control of airconditioning systems of the type in which a mixture of fresh and returnor recirculated air is exposed to the action of one or more conditioningunits preparatory to being discharged into the space to be conditioned.

The general object of the invention is to provide in a combined heating,cooling, humidifyi'ng and dehumidifying system a new and improvedautomatic control which is simple in construction, which is positive andreliable in operation, which maintains'the desired condition of thedelivered air with a high degree ofaccuracy, which.

insures optimum economy in operation, and which adapts itself quicklyand automatically to the requirements of the space being conditioned.

Another object is to provide a novel air cooling system and method ofcontrol "therefor in which the air outside of the building is utilizedto carry at least apart of the cooling load when its temperature is lowenough for that purpose.

A further object is to provide an all weather air conditioning systemincorporating a novel cont rol for insuring maintenance of the deliveredair at the proper temperature even though it must be pre-cooled, for thepurpose of removing excess moisture, to a temperature which would beuncomfortable to the room occupants.

Still another object' is'to provide a novel arrangement for preheatingthe mixture of 'fresh andreturn air preparatory to conditioning thesame. I

It is also an object to provide a novel mechanism for effectingactuation of a condition regulating member under the control of separatecondition responsive devices.

The invention also resides-in the novel man'- ner in which the openingand closing of the fresh air inlet is controlled to insure 'a-minimumdegree of opening thereof whenever the system is in operation.

Other objects and advantages of the invention will become apparent fromthe following detailed description taken in connection withtheaccompanying drawings in which 'Figures 1 and 2, when laid side by side,constitute a schematic view'and wiring diagram of an air conditioningsystem embodying the novel features of the present invention.

While the invention is susceptible of various modifications andalternative constructions, we have shown in th drawings and will hereindescribe ln detail the preferred embodiment, but

it is to be understood that we do not thereby intend to limit theinvention to the specific form disclosed, but intend to cover allmodifications and alternative constructions falling within the spiritand scope of the invention as expressed in the appended claims.

In the drawings, the invention is embodied for purposes of illustrationin a combined ventilating, heating, cooling, humidifying anddehumidifying system for discharging a mixture of fresh' and return orrecirculated air into a space 3 within a building having walls 4 andconditioning the mixture thus discharged so as to maintain predeterminedconditions of temperature and humidity in the space. A blower 5 inducesthe flow of fresh and return air through inlet ducts 6 and 1 into a duct8 having an outlet 9 from which the air is discharged into the space 3.Within the duct 8, the air mixture passes through a filter I 0 and thenis exposed to an humidifier II, a cooler l2, and a heater [3 which 'actsingly or in combination to condition the air properly. The blower isdriven by an electric motor H supplied with current from a high voltagpower source l5 under the control of a switch It. 1

The humidifier shown comprises a nozzle ll communicating through a pipeI8 having a valve l9 therein with a source of water under pressure andarranged to discharge a spray of water. into the air current wheneverthe valve is opened as will be the case when the winding 20 of asolenoid 2! thereof is energized. The humidifier will remain idle whenthe solenoid is deenergized.

. While any preferred form of artificial refrigeration means may beemployed, the cooler l2 shown herein comprises a. coil communicatingthrough pipes 22 with a source 23 of cooling fluid which is circulatedthrough the coil during operation of a pump 24 driven by an electricmotor. The motor is excited from the high voltage source whenever thewinding 26 of a relay switch 21 is energized.

The heater l 3 selected for illustration comprises a coil extendingpartially. across the duct 8 and supplied with heating fluid such assteam through a valve 28 arranged a modulating action posed in theby-passage 30 around the heater coil I3 is a damper 3| which is movedprogressively to be opened and closed with by an operator 29. Inter-Preferably, though not necessarily, the operator 32 is of the electrictype comprising a reversible electric motor 34 operating throughappropriate speed reduction gearing to drive a shaft 35 which carries acrank 35 connected by a link 31 to the damper 3|. The motor is of theshaded pole type having a main winding 38 with terminals connected topower conductors 39 and 39" leadin to a low voltage source 40. Mountedon the poles of the motor and arranged in pairs on diametricallyopposite sides of the rotor 4| are multiple turn shading coils 42 and 43which are arranged to be short-circuited selectively to cause the rotorto turn in opposite directions in a manner well understood in the art.

The valve operator 29 is constructed similar to the operator 32 andcomprises an electric motor 44 having a main winding connected to thePower conductors 39' and 39" and arranged to drive a shaft 45 carrying acam 46 by which the member of the valve is reciprocated. When shadingcoils 41 of the motor are short-circuited with the valve partially open,the rotor turns in a clockwise direction causing the valve to be closedslOWly. Similarly, the valve is opened progressively while shading coils48 are short-circuited and theooils 41 open-circuited. When both sets ofshadin coils are open-circuited, the position of the valve is maintainedfrictionally.

In the present instance, the position of the valve 28 is shifted tocorrespond to the heating requirements under different conditions. Tothis end, the operator 29 is controlled in accordance with the positionof the by-pass damper 3|, the arrangement being such that the valve willbe moved toward closed position when the by-pass damper reaches the fullcooling position shown, will move towardopen position while the damperis disposed in closed or full-heating position, and will be held infixed position when the damper is in any intermediate position. For thepurpose of effecting such control, the circuit for the shading coils 48is extended from the coils through The terminals of the main winding ofthe motor 5| are connected to the power conductors 39 and 33a, and thedirection of rotation of the operating shaft B2'is determined byselectively short-circuiting pairs of shading coils 55 and 66, thearrangement being such that the fresh air damper will be moved towardopen position when the coils 55 are short-circuited and toward closedposition when the coils 65 are short-circuited.

In a system'of the above character, the artificial cooling mechanism isthe most costly part to operate. The present invention aims toreduce thetime and therefore the cost of operation of the cooler |2 to a minimumby utilizing a conductor 50 having therein a limit switch 5| which isclosed except when the valve is in fully open position, a switch 52, theconductor 39, and an extension 49 of the conductor 39. A cam 53 on theshaft 35 is shaped to close the switch 52 when the by-pass damper 3|reaches closed position, the coils 48 being thereby short-circuited sothat the valve member will be moved away from its seat until it reachesfully open position as evidenced by opening of .the limit switch 5| oruntil the switch 52 is opened by movement of the by-pass damper awayfrom closed position. Similarly, the short-circuit for the shading coils41 is controlled by a-limit switch 54 which is closed except in theclosed position of the valve 28 and by a switch 55 which is held closedby a cam 56 when the Joy-pass damper 3| is in the open position shown.

The flow of air through the fresh and return inlets is controlled bydampers 51 and 58 dis- I posed in the respective inlets and connected bya link 59 for movement in unison, the fresh air damper being fullyclosed when the return damper is fully open as shown and vice versa.Progressive movement of the dampers between their limit positions iseffected by a power operator 60 which preferably comprises a reversibleshaded pole motor 6| geared to a main operating shaft 62 which isconnected by a crank 53 and a link 64 to the link 59. The range ofmovement of the dampers thus corresponds to a half revolution of theshaft 52.

the outside air to carry all or part of the cooling load whenever itstemperature is sufliciently low. For ventilating purposes, the inventionalso contemplates maintenance of the fresh air damper in at least apredetermined partially open position whenever the system is inoperation. To these ends, means are provided which operate, when theoutside air is below a predetermined useful value, for example 65degrees F., to control the operator 6!! and cause modulating movment ofthe damper between the minimum and fully open positions so as tomaintain the temperature of the air mixture at a value appreaching thatdesired for cooling purposes.

In the present instance, such operation is effected by controlling thecircuits for the shading coils B5 and 63 by the combined action ofswitches 61 and B8 of a magnetic relay having a winding 69 which isenergized whenever the fan motor I4 is running, by an insertionthermostat 10 responsive to temperatures in the fresh air inlet 6, andby a second thermostat 1| responsive to the temperature of the mixed airand having a thermostatic element which extends substantially across theduct 8 so as to respond to the average temperature of the mixture.

To maintain the fresh air damper open at least to its minimum positionirrespective of the condition of the thermostats 10 and 1| whenever thesystem is in operation, the operating shaft 62 carries a cam 12 whichoperates switches 13 and 14. When the fresh air damper is in closedposition as shown, the switch 13 is held closed and remains closed asthe cam turns in a clockwise direction during initial opening of thefresh air damper. As the dwell surface 15 of the cam 'passes beyond thefollower 16 as will be the case when the fresh air damper is openedbeyond its selected minimum position, the switch 13 is allowed to openand the-switch 14 is allowed to close. As will later appear, the switch14 acts to limit the position to which the fresh 'air damper may beclosed under the action of the thermostats 10 and 1| alone.

Assuming that it is desired, for cooling purposes, to maintain the airdelivered to the room at a temperature not lower than 60 degrees, thethermostat 1| would be set so as to close its switch 11 when the mixedair temperature is above 60 degrees and to close the switch 18 when thetemperature is below operating range of the thermostat. Since the freshair should ordinarily be below 65 degrees F., in order to be useful forcooling purposes in the present system, the thermostat 10 is set toclose its switch 19 above 65 degrees and to close its switch below thisvalue.

With the thermostats thus set, the fresh and ture is above 60 degrees,and that the system is not operating, the parts being positioned asshown in the drawings. When the fan is started by manual closure of theswitch IS, the switch 61 is closed which completes a short circuit forthe shading coils 65 of the damper operator 68. This circuit extendsfrom the shading coils through the conductor 39, the switch 6 aconductor 8|, the switch 11 of the thermostat 1|, a conductor 82, thethen closed switch 88 damper until the temperature of the mixture fallsbelow 60 degrees whereupon the short circuit for the coils 65 will bebroken by opening of the switch 11.

If, at the time the blower is started, the outside temperature is above65 degrees or the duct temperature is below 60 degrees, the shadingcoils 65 will nevertheless be short-circuited when the switch 61 isclosed, the circuit extending through the conductor 81, the closedswitch 13 and either the conductor 86 and the switch 18 or the conductor89 and the switch 19. Likewise, when the switch 61 is closed, theoutdoor air is sufficiently cool to reduce the duct temperature below 60degrees before the damper 51 reaches its minimum position, the shortcircuit for the coils 65 will be maintained through the switch 18, theconductor 86, the switch 13 and the conductor 81. In any of the threecases last assumed, the operator will stop when the damper reaches itsminimum open position, the switch 13 and either the switch 11 or theswitch 18 being then open.

If the temperature of the mixture falls below 60 degrees with the damper51 opened beyond its minimum position, the switch 18 will be closed, thecoils 66 being thereby short-circuited through a circuit extending fromthe conductor 8| through the thermostat switch 18, the conductor 86, thethen closed switch 14, and a conductor 88. The motor 61 then runs in adirection to close the fresh air damper and open the return air ductthereby increasing the temperature of the air mixture until 60 degreeshas been attained or the minimum position of the fresh air damperreached. As the temperature-of the mixture rises above 60 degrees, themovement of the damper will be reversed by closure of a short-circuitfor the coils 65 through the switch 11, the conductor 82, the thermostatswitch 80, and the conductors 83 and 85 and the switch 84.

It will be seen that while the fan is operated and the outsidetemperature is below 65 degrees, the fresh air damper will be oscillatedback and forth under the control of the thermostat 1| between the fullopen and a predetermined partially open or minimum position therebymaintaining the temperature in the duct 8 at 60 degrees provided theoutside temperature is below this value. If the latter is'between 60 and65 degrees, the fresh air damper will be moved to and remain in fullyopen position. If, due to a prolonged fall in the air temperature below60 degrees, the switch 18 remains closed until the fresh air damperreaches its position of minimum opening, the switch 14 will be openedand the closing movement of the damper arrested. When the outsidetemperature rises above65 degrees as evidenced by opening of the switchand'closure of the switch 19 of the thermostat 18, the-fresh air damperwill be moved to its position of minimum opening in spite of the factthat the thermostat 1| will be calling for a lower duct temperature andtherefore for more fresh air. Such movement is caused by closure of acircuit extending from the shading coils 66 through the conductor 88,the then closed switch 14, the conductor 86, the conductor 89, theswitch 19, the conductor 82, the switch 11, which will then be closed,to the conductor 8|. The operator 68 will thus close the fresh airdamper until the minimum position is reached whereupon the switch 14will be opened by the cam 1.2 thereby opening the shading coil circuitand arresting the closing movement of the fresh air damper.

The fresh air damper is moved to fully closed position independently ofthe thermostats 10 and II when the fan is stopped and operation of thesystem discontinued. This is effected by closure of the relay switch 68which completes a shortcircuit for the shading coils 66 extending fromthe .coils through the conductor 88, the then closed limit switch 9|, aconductor 98, the switch 65 and the conductor 39. The circuit is brokenby opening of the limit switch as the damper becomes fully closed.

From the foregoing, it will be seen that the control by the switches 61and 68 is superior to that of the thermostats 18 and 1| and that thethermostat 18 is capable of closing the fresh air damper to minimumposition while the thermostat 1! is calling for cooler air. Accordingly,the fresh air damper is closed when the system is idle, is always openat least to aminimum position when the system is in operation, ismodulated between the minimum and fully open positions when thetemperature outside is sufliciently low, that is below 60 degrees, toenable the outdoor air to carry the entire cooling load, remains infully open position when the outside air is sufficiently cool, that isbelow 65 degrees, to carry at least a part of the cooling load, and ismaintained in the minimum or partially open position when the outsideair is above 65 degrees. In this way, the cooler 12 will be called intooperation to handle only that portion of the cooling load which cannotbe supplied by the outside air under the conditions prevailing at thetime. Maximum economy is thus obtained in the operation of the systemfor cooling purposes, and the service life of the artificial coolingequipment is prolonged.

In systems of the present character, it is desirable to maintain arelative humidity of at least thirty per cent in the space beingconditioned. To accomplish this, means is provided for rendering thehumidifier operative whenever the relative humidity in the room fallsbelow the desired value. humidostat 93 having an element 94 disposed inthe space 3 andarranged to actuate a control switch 95, maintaining theswitch open when the relative humidity is above the value for which thehumidostat is set and closed when the humidity falls below this value.The switch is arranged in the circuit by which the winding 20 of thesolenoid valve 19 is energized and which extends from the power lead 39through the winding 20,

Herein, this means comprises an 99 and I will be closed respectivelywhen the room temperature is above and below the operating range of thethermostat. A call for heat I which will be evidenced by closure of theswitch I00 completes a short-circuit extending from the coils 43 througha conductor IOI, a limit switch I02, which is closed except when thedamper 3| is fully closed, a conductor I03, the switch I00, the tongueof the thermostat 98, the conductor 91, and the conductors 49 and 39.With the coils 43 thus short-circuited, the motor 34 rotates in aclockwise direction to close the by-pass damper and thereby increase theamount of heat imparted to the air by the coil I3. If the switch I00remains closed for a period of time sufficient to enable the damper toreach its fully closed position, then the resulting closure of theswitch 52 will initiate operation of the motor 44 to open the steamvalve 28 to a greater degree thereby increasing the capacity of theheater I3.

In response to closure of the switch 99 as the room thermostat ceases tocall for heat, the shading coils 42 are short-circuited through acircuit which extends through a conductor I04, a limit switch I05 whichis closed except when the damper 3I is fully opened, a conductor I06;

a then closed switch I01 of an. insertion thermostat I08 in the ductoutlet 3, a conductor I09, the switch 99, and conductors 91, 49 and 39.With the coils 42 thus efiective, the motor 34 runs counter-clockwise toopen the by-pass damper 3| and thereby decrease the amount of heatimparted to the air current flowing through the duct 8. In this way, thedamper will be oscillated back and forth under the control of thethermostat 98 whereby to cause the conditioned air to be heated to atemperature suffi cient to maintain the desired room temperature. Inaddition, the operator 29 is controlled in response to the movements ofthe by-pass damper in a manner such as to adjust the position of thesteam valve and throttle the flow of steam to the heating coil I3 so asto establish a rate of flow corresponding approximately to the pre'-vailing heating requirements. The thermostatic control of the dampersupplements the steam valve control and enables very accurate regulationof the conditioned air temperature to be obtained. I

When the cooling requirements of the space.

being conditioned cannot be satisfied by supplying fresh air thereto,the cooler I2 is rendered operative underthe control of a thermostat II4located in the room and adjusted to the temperature which is to bemaintained in the room when cooling is required. This temperature willbe several degrees above the setting of the heat controlling thermostat98 and ordinarily will be varied in any well known manner with changesin .the outside temperature.

The thermostat II4 has a switch H5 which becomes closed as the roomtemperature rises above the value for which the thermostat is set. Thisswitch controls an energizing circuit for the winding 26 of the relayswitch 2'! which circuit extends from the power conductor 39 through thewinding 26, a conductor IIS, 2. switch III ofa thermostat H8 in the ductoutlet 3, a conductor II9, the thermostatic switch II5, the conductors91 and 49 to the power conductor 39. Thus, when both of the switches H5and Ill are closed, the relay will be energized starting the pump andcausing cooling fluid to be circulated through the coil I2. The coolercontinues in operation until the room temperature has risen above thedesired value or until the switch III of the duct thermostat is opened.

The latter thermostat is arranged to respond I to changes in thetemperature of the air discharged through the outlet 9 and is set torespond to a limit value below which the discharged air would produceobjectionable drafts in the room. If the thermostat H8 is set for 62degrees F., for example, its switch would be opened and the operation ofthe cooler interrupted whenever the temperature of the conditioned airfallsbelow this temperature even though the cooling requirements of thespace as determined by the thermostat II4 have not been satisfied.

Preferably, the air stream thermostat II is adjusted to maintain atemperature of the mixed air slightly below the minimumlimit to whichthe cooler I2 may reduce the conditioned air as determined by thethermostat IIB. Thus, the artificial cooler is maintained idle by theaction of the thermostat II8 so long as the outdoor air is cool enoughto carry the entire cooling burden determined by the thermostat II4.

Whenever the relative humidity in the space being conditioned risesabove a predetermined maximum value, usually about fifty-five percent,means is provided for operating the cooler I2 irrespective of thecondition of the thermostat II4 so as to effect dehumidification of theair being discharged into the room. This means comprises an humidostatI20 in the room set to close a switch I2I whenever the humidity risesabove the maximum limit desired. The switch I2I is interposed in aconductor I22 extending between the conductor 91 connected to the powerconductor 39 and the conductor II6 leading to the winding 26 so thatwhenever the switch I2I is closed, the relay' switch 21 will beenergized and the flow of cooling medium to the coil I2 initiated.

In the event that the cooling effect of the coil I2 is increased underthe independent control of the humidostat I20, to such an extent as tolower the temperature of the conditioned air below that which isdesirable from the standpoint of avoiding drafts on the occupants, theheater I3 will be rendered effective to reheat the dehumidified air tothe proper temperature. This is accomplished in the present instance bythe action of the duct thermostat I08 which is adjusted so that itsswitch I23 will become closed in response to a minimum limit temperatureslightly lower, for example 60 degrees, than the value for which thethermostat H8 is set to respond. When the switch I23 becomes closed, theshading coils 43 will be short-circuited through the conductor I0 I, thethen closed switch I02, the conductor I03, a conductor I24, the switchI23, the conductor I09, the then closed thermostat switch 99 and theconductors 91, 49, 39 and 39. As a result, the motor 34 will be startedand the by-pass damper 3| moved toward closed position thereby causingheat to be supplied by the coil I3 and the rate of such supply to bincreased until the desired minimiun temperature of the'conditioned air,as d v 2,315,517 termined bythethermo'stat I08, has been at tained.

By virtue of this arrangement, the cooler I2 may be employed to performthe additional function of dehumidifying the air, theheater I3cooperating to prevent air, cooled to a low temperature for the purposeof dehumidification, from being discharged into the room at atemperature below GOdegrees.

dependently operable thermostats I08 and I I8 with the latter set'torespond to a temperature Such action is made possible in the presentinstance through the use of the inslightly higher than that for whichthe thermostat I08 is adjusted.

Under conditions sufficiently severe to prevent the heater I3, whenoperating at full capacity, from properly tempering the mixture ofreturn air and the minimum amount of fresh air, provision is made forpreheating the mixture before it reaches the heater. Preferably, this isaccomplished by supplying heat to the return air passing through theinlet 1 by means of a heating coil I supplied with steam or otherheating fluid under the control of a regulating valve I26. The positionof the latter is controlled by a thermoportion of fresh air admitted tosaid duct, a power operator for said damper means, a thermostatresponsive to the temperature of the mixture of fresh and return air andcontrolling said operator 'to modulate the position of a damper meansbetween said minimum open position and fully open position and maintaina substantially uniform temperature of the mixture, a thermostatresponsive to the temperature of the fresh air exercising control oversaid operator superior to said first mentioned thermostat and operatingto cause movement of said damper means to said minimum open position inresponseto a deviation in the fresh air temperature to a predeterminedvalue, and auxiliary control means operable independently of saidthermostats to control said operator and cause complete closure of saidfresh air inlet from any position in which the damper means is disposedat the time the auxiliary control means is rendered active.

2. In an air conditioning system having an air duct having fresh andrecirculated air inlets, a damper controlling the proportion of freshair admitted to said duct a power operator for movstat I21 responsive tothe average temperature of the air in the duct 8 and set to respond to atemperature several degrees, for example five, below the temperature forwhich the thermostat H is set. .Thus, when the weather is not toosevere, the airin the duct 8 will be maintained at 60 degrees under thecontrol of the thermostat 1|,

. while in extremely cold weather, the thermostat I21 will render theheater I25 operative to main- I tain the duct temperature at 55 degrees.

In the present instance, the valve I26 is actuated by an electricoperator I28-constructed similar to the' operator 2!! and having shadingcoils I30 and I3I adapted when short-circuited to cause the valve to beopened and closed respectively.

The circuits for the coils are controlled by limit.

switches I32 and I33 and switches I34 and I35 of the thermostat I21, thelatter being closedrespectively when the duct temperature is above andbelow the value for which the thermostat is set. Location of the preheatcoil I25 in the return air duct is especially advantageous in that thecoil is not exposed. to the incoming fresh air, and therefore there isno danger of the coil becoming damaged when the outside temperaturefalls below freezing with the preheat coil inactive.

It will be apparent from the foregoing that the controls above describedoperate entirely auto-,

matically under all conditions to maintain the desired conditions oftemperature and humidity in the space being conditioned and this inspite of the fact that the change from heating to cooling of the air mayoccur frequently in service. The various control mechanisms areinterrelated in a manner such as to operate positively and reliablyunder all conditions and to enable the amount and complexity of theconditioning units and of the control mechanism itself to be reduced toa minimum. At the same time, the system utilizes whenever possible thecooling effect of the outdoor air thereby providing for optimum economyof operation.

In the appended claims, the terms air condition are used to refer totemperature and humidity conditions only.

We claim as our invention:

ing said damper in opposite directions, a thermostat responsive to thetemperature of the air mixture and controlling said operator to modulatethe movements of said damper between positions of full and minimumopening of said fresh air inlet to maintain the predetermined minimumtemperature of said mixture, a thermostat responsive to the temperatureof the fresh air and exercising a control over said operator superior tosaid first mentioned thermostat and causing movement of said dampertoward closed position when the fresh air temperature rises above apredetermined value useful for cooling purposes, and means responsive tomovement of the damper and operating to interrupt the closing movementthereof under the control of either 'of said thermostats when the damperreaches said position of minimum inlet opening.

3. In a combined ventilating and cooling system having an air duct'andfresh and return air inlets, damper means controlling the proportiors offresh and return'air delivered to said duct,

means responsive to the temperature of the air mixture and regulatingthe movements of said damper means to maintain a substantially uniformtemperature of the air mixture, means responsive to the temperature ofthe fresh air and regulating said damper means independently of saidlast mentioned means to maintain a fixed minimum proportion of fresh airin the mixture when the fresh air temperature is above a predeterminedvalue useful for cooling purposes, and means controlling said dampermeans independently of said temperatureresponsive means to effectcomplete closure of the damper means from any position thereof.

4. In a combined cooling and ventilating system having a duct with freshand return air in- 1. In an air conditioning System having an air lets,damper means controlling the proportion of fresh air admitted to saidduct, a power operator for said damper means, a thermostat controllingsaid operator to cause opening of the fresh air inlet beyond a minimumdegree when the temperature of the mixture of fresh and return air isabove a predetermined value whereby the outdoor air may b utilized forcooling purposes, thermostatically controlled means controlling saidoperator independently of said thermostat to cause movement of thedamper and closure of said fresh air inlet to said minimum degree whenthe temperature of the fresh air rises above a predetermined value, andother means independently controlling said operator to "cause closingmovement of said damper means.

5. In an air conditioning system. the combination of means fordischarging a current of air into a space to be conditioned, a coolerand a heater each arranged in heat-exchanging relation with respect tosaid air current, a thermostat in said space controlling the operationof said heater to maintain a uniform temperature in the space whenheating of the space is required, 'a second thermostat in said spacecontrolling the operation of a cooler to maintain a predetermined highertemperature in the space when cooling thereof is required, an humidostatin the space adapted'to render said cooler operative independently ofsaid second thermostat when the relative humidity in the space risesabove a predetermined value, a third thermostat responsive to changes inthe temperature of the conditioned air and controlling said heater toprevent delivery of air to said space at a temperature below apredetermined minimum limit during operation of said cooler under thecontrol of said humid-ostat, and a fourth independently operablethermostat controlling said cooler and operating to limit thetemperature to which the conditioned air may be reduced to a valuehigher than said minimum limit.

6. In a combined ventilating and tempering system having an air ductwith fresh and return air inlets, valve means controlling the proportionof fresh and return air admitted to said duct, thermostatic meansregulating said valve means to admit varying amounts of fresh air andmaintain a substantially uniform temperature of the fresh and return airmixture, thermostatic means exercising a control over said valv meanssuperior to said first mentioned thermostatic means and regulating saidvalve means to reduce the proportion of fresh air in'said mixture to apredetermined proportion sumcient for ventilating purposes when theprevailingtemperature of the fresh air is such as to render the latterunsuited for tempering'pmposes, and means controllin said valvemeansindependently of both of said thermostatic means to cause completeclosure of said fresh air inlet from any degree of opening of the valvemeans.

'7. A control for air conditioning systems having, in combination, valvemeans controlling a passageway adapted for the flow of a conditioningmedium therethrough, a reversible power operator for actuating saidvalve means, means controlling said operator to cause uninterrupted thefurther opening of said passageway beyond said predetermined degree ofopening, and a-second independently operable temperature responsivedevice controlling said operator to cause closing of said passagewaytoward said predetermined amount from any degree of opening beyond suchdegree.

8. An air condition control having, in combination, a valve controllinga passageway and actuated by a member movable between passageclosed andpassage-open positions through a predetermined intermediate position, areversible power operator for said member including electric motordriving means having valve-closing and valve-opening windings, a firstswitch which is respectively closed and open when the member is aboveand below said intermediate position and a second switch which is closedand open when said first switch is open and closed respectively, aircondition responsive means having one switch controlling a circuit forsaid valve opening winding'independently of said switches and anotherswitch controllingsaid opening winding through the medium of said secondswitch and said closing winding through the medium of said first switch,and an automatic control device having one position in which said aircondition responsive means is rendered operative and a second positionin which said valveclosing winding is rendered active to cause movementof said member to said closed position independently of said aircondition responsive means;

9. An air condition control having, in combination, a valve controllinga passageway and actuated by a member movable between two limitpositions through a predetermined intermediate position, a reversiblepower operator for said member including electric motor driving meanshaving two windings respectively energizable to cause movement of saidmember in opposite directions, a first switch which is respectivelyclosed and open and a second switch which is respectively open andclosed when the member is above and below said intermediate position,air condition responsive means having third and fourth switchesrespectively closed by opposite movements of a reversibly movablecontrol element, a

circuit for one of said windings including said third switch, a secondcircuit for said one winding including said second nd fourth switches,and a circuit for the other of said windings including said first andfourth switches.

10. An air condition control having, in combination, a valve controllinga passageway and actuated by a member movable between two limitpositions through a predetermined intermediate position, an aircondition responsive device having acontrol element movable between twopositions, first and second switches respectively closed and open whensaid member is on one side of said intermediate position andrespectively open and closed when the member is disposed on the otherside of the. intermediate position, a reversible power operator for saidmember operable to cause movement of the member from one limit positionto said intermediate position independently of said switches when saidelement is in one of its positions and through the medium of said firstswitch when the element is in its-other position, said device coactingwith said other switch in causing reverse movement of the member when.

CERTIFICATE OF CORRECTION. Patent No. 2,515,517. April 6, 195.

THEODORE K. GREENLEE, ET AL. v

It is hereby certified that error appears in the printed specifieati onof the above numbered patent requiring correction as follows: Page5,-sec- 0nd column, line 5, for "a damper read sa.1d damper-; line 6,for "said minimum read --a minimum-; page 6, first collimn, line 614.,for amount from any degree" read -'-degree from any mount; ahd that theeaid Letters Patent should be read withthiscorrecti on therein that thesame may conionnto the record of the case in the Patent Office. I

Signed and sealed this lst day of June, A. D. 19h5.

Henry Van Ar'sd aIe,

'. (Seal) I Acting commissioner'offatents.

